1. Field of the Invention
The present invention relates to a variable inductance element, and more particularly, to a variable inductance element for use in a mobile communication device such as a mobile telephone or other suitable mobile communication device.
2. Description of the Related Art
In recent years, the size of mobile communication devices such as portable telephones has been substantially decreased, and demands for reducing the size of electronic components for use in the devices has substantially increased. Further, as higher frequencies are used in mobile communication devices, the circuits of the devices become more complex, and moreover, electronic components to be mounted in the devices must have uniform characteristics and high precision.
However, even where each electronic component included in a circuit has parameters with uniform characteristics and high precision, deviations in the parameters of the respective mounted electronic components have an overall or combined effect, so that in some cases, a desired function can be performed. Hence, some of the parameters of the electronic components included in an electronic circuit are variable, if necessary. By finely adjusting the parameters of some of the electronic components, a desired function of the circuit can be performed.
As a conventional trimming method for electronic components of the type described above, a method of trimming a variable inductance component, for example, as shown in FIG. 4 has been generally known. A variable inductance element 55 includes a trimming area 53 provided on the surface of an insulating substrate 50, connected to external electrodes 51 and 52, which is arranged to function as an inductor. The trimming area 53 is irradiated with a laser beam emitted from a laser trimming machine (not shown) while the beam is linearly moved. The trimming area 53 is partially removed corresponding to the movement track of the laser beam, so that a linear trimming groove 54 is produced. Accordingly, the area of the trimming area 53 is altered such that the inductance of the trimming area 53 is finely adjusted.
In the conventional variable inductance element 55, if the area of the trimming area 53 is relatively small, the variable range of the inductance is decreased, so that the circuit cannot be finely adjusted. Therefore, the trimming area 53 must have a large area. On the other hand, when a high precision laser trimming machine is used, the groove width (trimming width) of the trimming groove 54 produced by trimming once is relatively thin. For this reason, when a wide trimming width is required, irradiation with a laser beam must be repeated while the irradiation position is moved in parallel. Hence, the time required to achieve the fine adjustment is substantially increased.
Accordingly, a variable inductance element 65 is shown in FIG. 5. The variable inductance element 65 includes an inductor pattern 61 provided on the surface of an insulating substrate 50 and connected to external electrodes 51 and 52. The inductor pattern 61 is a ladder-shaped electrode including a U-shaped frame portion 61a and a plurality of lateral bars 61b arranged to cross two arms of the U-shaped frame portion 61a to be trimmed for adjustment of the inductance. The variable inductance element 65 is mounted on a printed circuit board or other suitable substrate, and is irradiated with a laser beam from above the variable inductance element 65, so that a trimming groove 54 is produced in the inductance element 65 and simultaneously cuts the lateral bars 61b of the inductor pattern 61 individually and sequentially. Accordingly, the inductance between the external electrodes 51 and 52 can be altered in a stepwise manner.
The inductance element 65 has improved cutting workability, since the lateral bars 61b are arranged at relatively wide equal intervals. However, the amount of change of the inductance, caused every time one lateral bar 61b is cut, is relatively large, since all of the lateral bars 61b have an equal length. For this reason, in the inductance element 65, the inductance cannot be altered equally in a stepwise manner. That is, fine adjustment of the inductance is difficult.
To solve this problem, a variable inductance element 75 is shown in FIG. 6. The variable inductance element 75 has an inductor pattern 71 including a U-shaped frame portion 71a and a plurality of lateral bars 71b extending across two arms of the U-shaped frame portion 71a. The lateral bars 71b are arranged at intervals that become narrower in a stepwise manner. Hence, the amount of change of the inductance, caused every time one lateral bar 71b is cut, remains substantially constant. However, in the inductance element 75, the intervals of the lateral bars 71b become narrower as the number of cut lateral bars 71b is increased. This increases the possibility that the lateral bars 71b may be erroneously cut, thus the adjustment of the inductance is difficult.
To overcome the above-described problems, preferred embodiments of the present invention provide a variable inductance element having a high Q factor, and in which the inductance is finely adjusted efficiently and accurately.
According to preferred embodiments of the present invention, a variable inductance element is provided including (a) an insulating substrate; and (b) an inductor pattern provided on the surface of the insulating substrate, (c) the inductor pattern being a ladder-shaped electrode having a substantially V-shaped frame portion and a plurality of lateral bars extending across two arms of the substantially V-shaped frame portion and arranged to be trimmed for adjustment of the inductance, the plurality of lateral bars being arranged at substantially equal intervals.
With the above-described configuration, the lengths of the respective lateral bars are sequentially decreased as the distance between the two arms of the substantially V-shaped frame portion is gradually reduced. Accordingly, when the lateral bars are sequentially cut in the order of decreasing length, the inductance of the variable inductance element does not change rapidly.
Preferably, the two arms of the substantially V-shaped frame portion have an angle of approximately 45xc2x0 relative to the lateral bars. Accordingly, magnetic fields generated in the respective arms are substantially perpendicular to each other, thereby eliminating mutual interference.
Other features, elements, characteristics and advantages of preferred embodiments of the present invention will become apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.